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Abstract

The invention relates to remote controlling equip- ment, such as remote keys for locks and alarm systems, having enhanced security.

Copyright

Motorola Inc. May 1992

Country

United States

Language

English (United States)

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MOTOROLA INC. Technical Developments Volume 15 May 1992

SECURE REMOTE CONTROL SYSTEM

by Jeffrey Wright and Mark Maiolani

The invention relates to remote controlling equip- ment, such as remote keys for locks and alarm systems, having enhanced security.

Many 'dumb' remote control systems exist, but these are not secure as the codes transmitted are fmed. For example, a car thief can intercept the futed code transmitted by a car owner and then at a later date, use the intercepted code to unlock the car. Existing microcontroller based solutions are more secure than these 'dumb' systems since they transmit a changing code. However, in order to send a changing code, non- volatile memory (NVM) must be employed in the trans- mitter which increases the cost and power consumption of the system.

The invention overcomes these problems by using a microcontroller with on-board random number gen- eration to transmit an encrypted ever changing code that can be decrypted and verified by a receiving device.

Referring tp Figure 1, the information to be transmitted is obtained by the transmitting MCU 2. The information comprises a code stored in the MCU 2, for example by way of an input pin matrix. The MCU 2 also obtains a random number either from s&ware or from an on-chip random number generator. This number is then com- bined with the information in an encryption algorithm. The encrypted output is the data that is transmitted to the receiving device 4. Each time information is trans- mitted to the receiving device 4, the MCU uses a new random number. This procedure results in the trans-